DARPA aims to make renewable power practical at last

At Afghanistan combat bases, anyway

Pentagon boffinry bureau DARPA, which deals with established technology paradigms in much the same way as Patrick Swayze and Demi Moore dealt with clay in their 1990 supernatural romanta-flick outing - that is as material for squidging into improbable shapes so as to satisfy the squidger's raging occult lusts - has done it again.

In this case the deep-seated desire which DARPA is trying to satisfy is the need to remove a major obstacle facing renewable power sources. As the war-boffins put it in a request for proposals issued yesterday:

For example, using photovoltaics for power generation, a short-term interruption could be caused by a cloud passing in front of the sun, a medium term interruption would be caused by the sun setting, and longer term power interruption could be caused by a multiday storm or seasonal event. Available wind power manifests power fluctuations of similar timescales.

This means that something else must be ready to step in when renewable power gets interrupted. This could be conventional fossil-fuelled (or nuclear) "thermal" generation. This is mostly what happens when major grid-scale renewables kit suffers interruptions.

But having full thermal backup for renewables is expensive: it makes the idea of renewables much less attractive once you are using renewables for a large amount of your load, both on a grid - or at a US military forward operating base in a warzone. At the moment such US bases are powered largely by diesel generators, meaning that fuel has to be trucked in along roads plagued by ambushes, mines, bombs - and occasionally by recalcitrant neighbouring governments.

This has previously led DARPA to look at powering such bases with small nuclear reactors, which could have the added benefit of perhaps allowing vehicle and aircraft fuel (another big logistics burden) to be produced locally from soldiers' poo using surplus reactor power.

However, another plan which has lately been gaining much currency across the US services is the installation of solar or wind power at FOBs.

Thus it is that DARPA plans a project called Deployed Energy Storage (DES) to store surplus power from the renewable generators when output is high, and use this stored juice to make up the shortfall when the sun goes in or the wind drops.

This will be amazing stuff indeed:

The system at full charge will be capable of providing uninterrupted power to a 150 kW average load for 9 days with 90% reduction and 30 days with a 30% reduction in available generated power from an appropriately sized renewable power generation plant.

Or in other words the kit will be capable of holding and releasing no less than 32.4 megawatt-hours, and will laugh at fast charge/discharge rates and rapid charge cycles. And it will be deployable to a military FOB, so it has to be something that fits on a reasonable number of trucks.

Some power utilities have tried using large, specialist li-ion battery installations in such tasks. Typical installations can hold 500 kilowatt-hours and fit into a truck trailer: to meet DARPA's requirements one would need a fleet of 60 or 70 trucks to deliver the DES kit.